This invention is directed to an apparatus and method for providing spatially-selective on-line mass or volume measurements of manufactured articles. More specifically, it pertains to the use of optical emitters, detectors, and field-of-view (FOV) limiting optical elements to provide a system for monitoring the volume or mass of material contained within a prescribed region of a discretely manufactured part. The system makes mass or volume measurements on dynamic parts, typically as they are being fabricated and/or conveyed in a manufacturer's plant.
While the invention is particularly directed to the art of high-speed automated product measurement, process control, and inspection, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention will also find useful application in a wide range of environments where non-destructive and comprehensive measurement of physical parameters is desired.
The use of sensor-based instrumentation to deduce the amount of material being consumed or applied by an industrial or commercial process is well known in the art. As a most basic example, the fuel gauge of an automobile provides the operator of the vehicle with a real-time measure of the amount of fuel remaining in its gas tank. Similar process monitors, whether they be tuned to measure volume, number or mass, are deployed in a vast number of manufacturing operations in a wide number of industries.
The use of sensor-based mass or volume measurement instrumentation to quantify the mass or volume of individual articles which are either produced or handled by an automated operation are not as widely known. However, examples do exist. U.S. Pat. No. 4,486,136, entitled “Device for Determining Weight of Objects Being Moved,” describes a system which determines the weight of logs, poles, or beams as they are being moved by a loader.
What is more typical, especially in those cases of high-speed manufacturing or conveyance operations, is the use of statistical product sampling and off-line quantification techniques. Using this manufacturing philosophy, a small percentage of the product that is manufactured or handled is diverted off the manufacturing line wherein its mass, volume or other attributes are quantified to a high degree of accuracy. This information is then used to deduce the quality or status of the product and/or manufacturing process.
In industries related to the manufacture of containers (food and beverage containers in particular), this model is generally followed. Containers are discrete items that are manufactured at high-speed. The amount of material used to construct a given item is an important manufacturing control parameter that effects the viability, quality, and profitability of the operations. The proper volume and distribution of material within a formed container is critical to the manufacturer's success in forming and selling the part. As such, the container industry has deployed a number of container measurement techniques that assist in determining whether manufacturing operations are in proper control. As an example, U.S. Pat. No. 5,591,462 describes the integration of a camera-based visual inspection system into a stretch blow-molding system used to form polyethylene terephthalate (PET) bottles. The inspection system is used to check for structural container defects such as holes or chipped sealing surfaces. This system is described as operating on-line as the containers are being inspected. In this capacity, it is capable of inspecting 100% of the parts being manufactured. This system does not have any means to determine or measure the mass or volume of the component under test.
U.S. Pat. No. 3,684,089, entitled “Container Wall Thickness Detection,” describes an instrument that can be used to gauge the thickness of the walls of a formed container. This system is based on capacitance sensing. It requires that the instrument come into direct contact with the object to be quantified. Many improvements to this basic technique can be identified in the prior art. All these related developments provide useful off-line characterization of the distributed material contained within a sampling of formed containers.
Similar off-line measurements of the wall thickness of formed containers can be made using infrared absorption techniques. U.S. Pat. No. 4,304,995, entitled “Method and Apparatus for Measuring the Wall Thickness in a Plastic Article,” describes a system that is used to measure the wall thickness of a hollow rotation-symmetrical plastic article. It performs this measurement by inserting a reflecting means inside the article under inspection and using this reflector to re-direct infrared energy emitted from outside the article onto a detector also located outside the article. U.S. Pat. No. 4,510,389, entitled “Infrared Film Thickness Gage,” describes a similar instrument but the source of infrared radiation is located inside the article under inspection and the detection means is located outside the article. In either case, the requirement to physically insert something within the article or container in order to facilitate the measurement makes these techniques practical and useful only in off-line sampling of the manufactured product.
U.S. Pat. No. 5,291,271, entitled “Measurement of Transparent Container Wall Thickness,” describes an apparatus which is used to measure the wall thickness of a container at a specific point. This system is based on the operation of a laser and a detector array which are used to measure reflections off both the outer and inner surface of a transparent container. In doing so, the thickness of the container at the entry point of the laser can be deduced.
Another process control operation, which is widely used in the PET container manufacturing industry, is off-line container sectioning and weighing tests. Containers which are produced by a manufacturing process are sampled—a few every hour or shift, depending on the plant's quality control plans—and diverted to a destructive testing process. There, the containers are generally cut into 3 parts: the base region, the sidewall region, and the opening or finish region. The mass of the PET material contained in these 3 general regions of the container are determined using a scale and the values recorded. The amount of plastic contained in these 3 general regions of the container is an important indicator to the plant operators of the real-time quality of the container manufacturing operations.
Over the years, the base mass or, alternatively, sidewall mass has become a well-understood attribute indicative of the quality of the manufacturing process. More specifically, the amount of PET material resident in specific portions of the container (such as the base region or the sidewall region) is indicative of whether the containers are being properly formed by the stretch blow-molding process. In order for the container to meet quality standards which have been established for it, the PET material which is contained in the molded preform blank (this entity is the start of the bottle forming process) needs to be properly re-distributed throughout the finished container. Again, the act of quantifying the mass of the PET material in general regions of the container using bottle sampling and sectioning techniques is a frequently used technique by the manufacturers of these items. It provides useful, but not timely, information that allows them to improve the quality of their manufactured product and increases their profitability.
Currently, there are no known methods of providing spatially-selective mass or volume measurements on 100% of formed containers, such containers being manufactured or conveyed in a manufacturer's plant. Heretofore, technical limitations have made it virtually impossible to obtain on-line mass or volume measurements that are essentially equivalent to the type provided using off-line sectioning and weighing techniques.